Woodpecker (Picidae) diversity in borer- Hoplocerambyx spinicornis infested sal Shorea robusta forests of Dehradun valley, lower western Himalayas Arun P. Singh Singh, A. P., 2010. Woodpecker (Picidae) diversity in borer- Hoplocerambyx spinicornis infested sal Shorea robusta forests of Dehradun valley, lower western Himalaya. Indian Birds 6 (1): 2–11. Arun P. Singh, Entomology Division, P.O. New Forest, Forest Research Institute (ICFRE), Dehradun 248006, Uttarakhand, India. Email: [email protected]; [email protected] Manuscript received on 14 August 2009. Introduction Relationship between woodpeckers and Cerambycidae The sal heartwood borer Hoplocerambyx spinicornis Newman beetles (Coleoptera: Cerambycidae) [sal borer; Fig. 1] is known to cause Woodpeckers (Picidae) feed on adults, grubs, and pupae of considerable mortality of sal Shorea robusta trees all over the latter’s wood-boring beetles that infest tree trunks and branches in forest distributional range in India. Explosive outbreaks of this insect, habitat (Ali & Ripley 1987). A notable influx of woodpeckers killing millions of trees over vast stretches of forests (Fig. 2), have accompanies an epidemic of borers in natural forests (Beeson 1941; been reported from time to time, from as early as 1897 (Stebbing Dennis 1967; Stoddard 1969; Jackson 1988, 2002). Woodpeckers 1899), to as recently as 2001 (Bhandari & Rawat 2001): from Assam are often cited as the most important predators of wood-boring 1906–1961; West Bengal 1931–1934; Bihar 1897; Madhya Pradesh cerambycid larvae (Brooks 1923; Linsley 1961; Solomon 1968, 1972, 1905, 1923–1928, 1959–1963; Uttar Pradesh: Kalagarh (now in 1974; Jackson 2002). It is possible that larvae near ground level, Uttarakhand) 1924–1925, 1934–1937; Himachal Pradesh 1948–1954 and near branch points within the canopy, are less vulnerable (Roonwal 1977). The sal borer generally attacks trees that are to woodpecker predation than those in a clearly exposed small- dead or practically dead, i.e., felled, victims of windfall, struck by diameter tree trunk. Similarly, adult beetles on the exposed lightning or broken by storms, or damaged, or attacked by root trunk may be more vulnerable to woodpecker predation while fungus. Healthy standing trees are not attacked unless there is an ovipositing, which may take up to half an hour or more. Apart epidemic of the borers, and the beetles are so numerous that the from small-sized beetles, and vegetable matter such as berries dead trees are insufficient for them (Beeson 1941). Sal heartwood and seeds, cerambycid grubs form the main diet (38%–46%) borer is today the major factor responsible for the decline of sal, of large-sized woodpeckers like the Ivory-billed Woodpecker besides other biotic, and abiotic factors such as intensive grazing, Campephilus principalis in North America (Jackson 2002). Predatory lopping, felling, etc., which hinder its natural regeneration. woodpeckers, e.g., Three-toed Woodpecker Picoides tridactylus, are also known to play a significant role in regulating bark and longhorn beetle populations in coniferous forest landscapes in Europe (Fayt et al. 2003). A positive correlation has been established between the abundance of longhorn beetle larvae, and the brood- size of woodpeckers —the Three-toed Woodpecker nestlings’ main Arun P. Singh Arun P. Fig. 1. Specimen of a male sal heartwood borer Hoplocerambyx spinicornis collected from Dehradun valley. Fig. 2. Extent of sal mortality caused by the sal borer. 2 Indian Birds Vol. 6 No. 1 (Publ. 25th June 2010) Singh: Woodpeckers & sal borer food (Fayt et al. 2003). Three-toed Woodpecker is also known to forests (Figs. 23, 24) (FSI 1995). These forests have a history of show the greatest numerical response to beetle prey density, with sal borer outbreaks all over the valley. Here, during 1916–1924 population densities increasing up to 44.8-fold during outbreaks, an outbreak at Thano range covered 18 km2, and over 80,000 relative to those supported at endemic beetle levels (Fayt et al. trees perished. During 1952–1953, again at Thano, 8,475 badly 2003). Some species of large-sized woodpeckers, like Black-backed infested trees had to be felled. In 1958–1960 an outbreak at Timli Woodpecker P. arcticus, which is extremely specialized in its range destroyed 12,860 trees. In 1961 in Lachhiwala range a ‘light’ foraging niche, feed exclusively by excavating larval wood-boring outbreak was reported. Then in 1965, once again in Thano range, beetles during outbreaks in dying conifers for only 2–3 years after 4.8 km2of forest was affected with 2,379 being trees attacked, forest fires in Alaska (Murphy & Lehnhausen 1998). followed by 21% infestation of trees by the borer during 1976–1978 Thus, woodpeckers are important bio-agents that feed on (Roonwal 1977; Singh & Mishra 1986). Recently, during 2000–2002, cerambycid borer larvae and pupae in natural forests, on old large-scale mortality of trees has occurred again, due to sal borer aged trees, and help in suppressing population of this pest to attacks in the valley (pers. obs. of author). some extent. However, extensive study is required to establish a similar Material & methods relationship between the sal heartwood borer and woodpeckers Selection of study sites in the tropical moist deciduous sal forests of the lower western Topographic maps and satellite imagery (IRS-IC 1998) data of the Himalayas. With this aim, the present study was carried out to study area, depicting the extent of sal forest cover in Dehradun evaluate the intensity of sal heartwood borer infestation in sal valley, were procured from Forest Survey of India (FSI) and Survey stands and examine the relationship of borer infestation with of India, Dehradun for selection of study sites (Fig. 3). Areas of sal abundance and diversity of woodpeckers. 2 forest covering more than 4 km , and with a canopy cover > 50%, were identified as potential sites for study. Fifteen forest ranges Study area with large sal forest tracts were thus identified as suitable for this Dehradun valley, which covers an area of c. 2,000 km2 and lies study. Based on the ground surveys nine sal forest sites (eight in in the lower western Himalaya in the state of Uttarakhand, was reserve forest area and one inside Rajaji National Park) distributed selected as the study area to work on this problem. About 51–58% all over the valley were marked and identified for sampling(Fig. land area in the valley was under tropical moist deciduous sal 3; Table 1). Field surveys were then carried out for collecting Arun P. Singh Arun P. Fig. 3. Dehradun valley: study area, the extent of sal forest cover and location of study sites as mentioned in the text. Indian Birds Vol. 6 No. 1 (Publ. 25th June 2010) 3 Singh: Woodpeckers & sal borer for sampling occurrence of woodpecker species. All woodpecker species up to 25 m on either side of transects, were identified and their numbers recorded. Nine sampling surveys were carried out at each site from May 2004 to February 2006, and February 2007, covering all the seasons. Woodpeckers were identified with the help of various field guides (Ali & Ripley 1987; Grimmett et al. 1998; Kazmierczak 2000; Rasmussen & Anderton 2005). Plants in vegetation plots were identified with the help of Kanjilal (1969), and the plant taxonomist at the Herbarium, Botany Division at FRI, Dehradun. Analysis Relative abundance of woodpeckers, computed as average of their abundances across samples for each site, was correlated with percentage of borer-infested sal trees using Pearson’s correlation coefficient. I also did regression analysis to model the relationship Arun P. Singh Arun P. between woodpecker species and sal-borer occurrence. Species diversity of woodpeckers (H’) was calculated from the Shannon Fig. 4. Grey-headed Woodpecker Picus canus. Index as follows (where pi is the proportion of the ith species in the sample): baseline habitat data for these study sites namely, percentage of Σ H’ = - pi loge pi borer-infested sal trees; tree girth at breast height (GBH); density per hectare, and tree species composition of sites. These were Shannon Index is essentially a combined measure of both determined by laying down 16 vegetation plots (quadrates of species richness (i.e., number of species) and evenness of 10 × 10m) in each site. Total numbers of sal trees were then counted abundances (i.e., how equitably all the species are distributed in in each plot, and were separated into borer-infested (including terms of their population) in a sample. In other words, species dead ones) and un-infested sal trees, to calculate percentage of diversity will be the highest in an assemblage of woodpeckers borer infestation. with a large number of species and with all the species occurring in high yet equal numbers. Woodpecker surveys The structure of woodpecker assemblages and their habitat Woodpecker surveys were carried out at each site visually, selection were studied by Principal Components Analysis (PCA), using binoculars and field guides. At each site, a transect of one which seeks to reduce a large number of species or ecological kilometer was marked through the forest, and walked through the factors into a few meaningful dimensions for easy interpretation. vegetation plots for 60 min., at a stretch, between 0800 and 1700 hrs I first generated a ‘site plot’ where the sampling sites were Table 1. Site parameters: vegetation and habitat condition of forest stands in Dehradun valley. Shannon Percentage of Percentage Sl. Dominant Diversity Site/Range Vegetation borer infested of trees with no. GBH class (cm) Index of sal trees GBH > 100cm Woodpeckers* 1 Kansrao Pure sal and mixed patches with marshy Low (1.7) 72 101-125 0.737 (Rajaji NP) vegetation having Trewia nudiflora ; Syzygium cumini 2 Karvapani Mainly mixed sal patches and marshy High (20.3) 56 76-100 0.823 RF vegetation having Sapium somniferum; S.